Mediterranean Freshwater Crab

Adult Potamon fluviatile may reach a carapace length of 50 millimetres (2.0 in), with females being generally smaller than males. As with other crabs, the body is roughly square, with the reduced abdomen tucked beneath the thorax. The thorax bears five pairs of legs, the first of which is armed with large claws.

The life span of P. fluviatile is typically 10–12 years. Moulting does not occur in winter. Mating lasts between 30 min and 21 hours, with spawning usually taking place in August. Females carry the eggs on their pleopods (appendages on the abdomen) until they hatch directly into juvenile crabs, having passed through the larval stages inside the egg.

The natural range of Potamon fluviatile is highly fragmented, and covers parts of many countries with a Mediterranean coastline. It is found in mainland Italy and on the Balkan Peninsula from Dalmatia to the Axios River in Greece. It is also found on a number of islands, including Sicily, Malta and Gozo, the Ionian Islands, Aegean Islands, Sporades and Andros in the Cyclades. Although the species as a whole is widespread, it is declining in numbers, and these insular populations are particularly vulnerable.

Potamon fluviatile has a generalist diet, feeding on vegetable debris, scraping algae from surfaces, or preying on frogs, tadpoles, and various invertebrates, such as insect larvae, snails or worms. No predator seems to specialise on P. fluviatile, but a number of animals take it opportunistically, including rats, foxes, weasels, wild pigs, otters, birds of prey and jays. The most significant predator may be mankind, with individual prospectors able to catch 3,000 to 10,000 in one season.

Adults occupy burrows, while smaller individuals shelter under stones. The entrances to the burrows may be more than 5 m (16 ft) from the stream's edge and are always above water level. The burrows may be more than 80 cm (31 in) long, and probably serve to protect the crabs from extreme cold.